There has been much recent progress in the field of power transistors, such as LDMOS (lateral double diffused MOS) power transistors with low "on-resistance" (Rds.sub.ON), and RESURF (reduced surface field) devices. Please refer to Appels, J. A. and Vaes, H. M. J., "High Voltage Thin Layer Devices (RESURF Devices)," IEDM Tech Digest, pp. 238-241, 1979, for a more detailed description of the RESURF technology.
Power devices are typically used in two circuit configurations, as a low side driver or a high side driver. In a low side driver circuit configuration, the drain of the power device is coupled to the power supply through a lead circuit, and its source is coupled to ground. In a high side driver circuit configuration, the drain is coupled directly to a power supply, and the source is coupled to ground through a lead circuit. RESURF LDMOS transistors are commonly used in the low side driver configuration because the source is structurally coupled to the substrate which in turn is coupled to ground. Therefore, these power devices are not used in high side driver applications and other applications where electrical isolation between the source and substrate is desirable.
Accordingly, it is desirable to provide a high voltage device with electrical isolation between source and substrate to be used as a high side driver. Additionally, it is necessary that such high power device exhibit low on-resistance (Rds.sub.ON) characteristics.